The present invention is concerned with improvements in or relating to heat setting, in particular the heat setting of shoes in the course of manufacture. The word "shoe" is used herein generically to include outer footwear generally whether completed or in the course of its manufacture.
Heat setting is an operation frequently performed in the manufacture of shoes to hasten shape retention of a lasted shoe upper and thus reduce the time the shoe has to remain on the last. A satisfactory heat setting technique entails relieving the stresses set up in a shoe upper which has been lasted. Radiant heating has been used for heat setting purposes but entails a danger of localized overheating and discoloring of some upper materials. A common prior heat setting technique comprises subjecting lasted shoes to a humid and then a dry atmosphere. There is disclosed in United Kingdom patent specification No. 1,081,613, for example, a method of setting a lasted shoe upper in which a lasted shoe is passed through a first chamber in which a humid atmosphere is provided, and then through a second chamber in which hot dry air is circulated.
While in said specification it is stated that hot air is directed into the second chamber at a velocity of about 75 feet per second (about 23 meters per second), it is found that by the time the air reaches the surface of a shoe upper being treated the actual air velocity is only 2 meters per second or less.
The apparatus described in said specification is somewhat complex and expensive, and in general use requires, when utilizing a humid atmosphere followed by a dry conditioning atmosphere, about 5 minutes treatment of a shoe to produce an acceptable degree of set of the shoe upper.